Variation of nitrogen species in zeolite-templated carbon by low-temperature carbonization of pyrrole and the effect on oxygen reduction activity

Nitrogen-doped microporous carbons with various compositions of pyridinic, pyrrolic, and graphitic N species were synthesized by the pyrolysis of pyrrole using Ca2+ ion-exchanged Y zeolite as a template. The Ca2+ ions in zeolite pores served as a catalyst to lower the carbonization temperature, resolving the problems associated with high carbonization temperature, such as inhomogeneous carbon deposition, easy breakage of weak C-N bonds, and preferential formation of thermodynamically stable graphitic N species. The resultant carbons exhibited a 3D microporous structure with high surface area and uniform micropore diameters, as well as high N content (5-6 wt%). Taking advantage of the lowered carbonization temperature, the ratio of the N species was modulated by the carbonization temperature, while a similar pore structure of the carbons was maintained. These N-doped carbons were used to investigate the efficiency of each N species on the electrochemical oxygen reduction, without the influences from the porous structure of the carbons. The results of this electrochemical investigation indicate that the graphitic N was more effective in enhancing the oxygen-reduction performance of the 3D microporous carbons than pyridinic N.